Tuesday, October 16, 2012

Do the spider dance!

This orb weaver is decorating for fall! Photo by Kirsten Pisto/Woodland Park Zoo.

Spider webs appear everywhere; draped across your porch, athwart your
front door, and if you happen to be tall, most likely dangling in your hair.
Despite the unpleasantness of being greeted each morning with a silky web stuck
to your face, orb weaver spiders are pretty incredible.

There are more than 3,000 different species of orb weavers around
the world, but the most common species in Western Washington is the cross spider
(Araneus
diadematus). These tiny architects are unbelievable weavers.

A female spider suns herself in the middle of her web. Photo by
Kirsten Pisto/Woodland Park Zoo.

Orb weavers construct their webs by first flinging themselves into
the breeze. Attached to an anchor point, the spiders float through the air
until they find a secure spot to dock. After the main line is attached, they
drop a second line from the center, forming a “Y” shape. This is the foundation
for the rest of the web.

You can see why the pattern on this cross spider earns its
name. Photo by Ryan Hawk/Woodland Park Zoo.

The spiders then begin to weave radii along a spiral path with
non-sticky silk. When they are done with the framework, the spiders will add a
sticky, capture silk to the radii over the dry web. So, the only parts of the
web that are sticky are on the radial web.

A dew-dropped beauty! Woodland Park Zoo archive photo.

So, how do the orb weavers escape getting caught up in their own web? First, orb weavers are careful to tip toe across their webs, they don’t slam into the sticky net like the other insects that become prey. Second, if they do make contact with the sticky portion of the web, they have secret tiny hairs on each leg called setae. The setae are short, bristly, and grow in irregular rows, so they easily pull away from any contact with the sticky adhesives. And last, researchers suspect that spiders actually coat their legs in an oily substance that repels their own glue, like being licked by a Teflon pan! (You can read
more about that study here.)

Detailed view of a female cross spider’s legs, you can see the
tiny setae hairs if you look close. Photo by a brave Ryan Hawk/Woodland Park Zoo.

Orb weavers usually sit at the center of the vertical web, with
their head facing down. They can feel the vibrations throughout the signal line,
so if an insect lands in a far corner of the web, the spider knows right where
to run first. Orb weavers can decipher the vibrations of a falling leaf from
the vibration of a flying insect, so they don’t waste energy.

In this awesome photo, an orb weaver has caught a bee and is
carefully wrapping it in a gossamer sack. Photo by Ryan Hawk/Woodland Park Zoo.

Once the spider gets the signal from its web, it will bite the
unlucky target and wrap it in silk. Then the spider waits for the prey to die,
vomits digestive fluid over it and… dinner is served! The treat is chewed with
the chelicerae (jaws) and the liquefied meat is sucked into its mouth. Mmm,
hungry yet? Spiders repeat this manner
until all but the inedible hard parts are left.

Many orb weavers actually rebuild their webs daily. If rain or wind
damages the web, the spiders will remodel. At dusk, some orb weavers consume their web to
conserve protein. They sleep for a bit, and then rebuild the web at daybreak.
This is why web-to-the-face syndrome usually occurs in the morning.

This pretty little orb weaver has tucked itself into a
flower petal for a nap. Photo by Kirsten Pisto/Woodland Park Zoo.

Orb weavers are around all year, but we tend to forget about them
until September, when they are large enough to lay eggs and spin larger webs.
Most of these spiders will die in the winter, but their new eggs will hatch
next spring.

The golden silk orb-weaver sits contently on her web in Bug World. Nephila madagascariensis is closely related to the common cross spiders here in the Pacific Northwest. Photo by Dennis Dow/Woodland Park Zoo.

At the zoo, our largest orb weaver is not one stretched across the
paths. Housed in Bug World, the golden silk orb weaver, Nephila madagascariensis, can grow as big as your hand! Visitors often remark at the windowless exhibit, but don’t worry; she’s happy where she’s at!

This web is extremely dangerous and should only be approached by
expert spider web wranglers. Photo by Kirsten Pisto/Woodland Park Zoo.

Bring your spidey senses and see how many orb weavers you can spot on your next trip to the zoo… just don’t get too close!

Enjoyed the article & pictures. I've spent hours watching spiders weave their webs. One interesting phenomenon: a spider built her web across my back door, which of course I walked through...after having it destroyed three days in a row, I noticed on morning four that it was now located diagonally in the upper corner of the door, well above the height of my head! And that's where she continued to build it. Pretty smart and adaptive little spider! Ruth in Ballard